The Asiatic Black Bear

The Asiatic, or Tibetan, black bear, Ursus thibetanus, is in many ways very similar to its cousin, the American black bear, even though the two species have evolved separately for over three million years.  At that time their common ancestors lived in western Asia, perhaps in the area of the Russian far east and further south.  During a glacial period over three million years ago when sea levels were low,  bears from the northernmost population must have expanded across the Bering Land Bridge to the New World and occupied the areas above the ice sheets.  During these interglacial periods, the Land Bridge and the area that it connected (also referred to as Beringia) was a fairly flat area, rising gradually to meet what are now the edges of the continents.  Depending upon the climate, the vegetation varied from grasslands to tundra.  In a few places there were even pockets of spruce forest; where fossilized spruce pollen has been found.  It was probably during one of the cold periods, when the climate was mild enough to support spruce, grasses, and grazing mammals, that the early black bears moved into Beringia and beyond.  These conditions must have lasted for many thousands of years.

As the sea levels rose, the group of bears in the New World became isolated and were probably stranded in eastern Beringia for some time, just as brown bears were at the end of the Pleistocene era.  As continental glaciers receded, the ancestral American black bears began expanding southward.  The black bears in Asia probably expanded their range southward and eastward as the climate changed.  What happened after that is difficult to know for certain.  American black bears and Asiatic black bears are considered to be sister taxa; they are more closely related to each other than to any other living bear species.  At some point, about 5 million years ago, they had a common ancestor.

At about that time, Asiatic black bears must have occupied the western coast of Asia from what is now the Russian Far East to what is now Malaysia.  They may have also occupied areas eastward, at least to the south of what is now the Gobi Desert.  During warm periods, this vast desert must have been as dry, or drier than it is now.  During one or more cold periods, the Asiatic black bears colonized the islands of Japan. They probably first reached the Japanese islands at about the same time that they crossed over to the New World.  During subsequent cold periods, bears probably migrated back and forth between the Japanese islands and the Asian mainland.

The current distribution of Asiatic black bears is divided into two large areas.  One group in southeast Asia extends from Malaysia, through the Himalayas as far as Pakistan, Iran, and Iraq.  The easternmost point of their range is in the Makran range of the Sarbaz mountains of southwestern Iran.  By the late 1960's they were considered extinct in Iran, but some were seen there in the 1980's.  The other black bear group is found along the western Asia coast and includes Japan, Korea, and the Russian Far East.  Asiatic black bears are found as far north as southern Siberia.  These two groups may have become divided only recently by the spread of human populations.  Bears have probably been excluded from the central portion of their historic range, western China, only since the rise of agriculture about 8,000 years ago.  Since that time, most black bear habitat has become fragmented by human occupation and conversion to agriculture, and humans have increased greatly in numbers.

It is likely that Asiatic black bears occupied all of these islands at one time or another until they were displaced by brown bears on Sakhalin and Hokkaido.  They live today even on the outskirts of Tokyo.  They are also found on the heavily populated island of Taiwan which they probably reached during an ice age in the Pliocene or before.  In these urbanized areas they are secretive and largely nocturnal, living in fairly small patches of rugged terrain and foraging at night in croplands and orchards as well as on native berries and nuts.

In areas near forests, where bears are at risk, farmers are encouraged to plant crops that will not attract bears.  Asiatic black bears are primarily found in broadleaf forests where acorns are one of their principal fall foods.  These native broadleaf forests have been increasingly cleared and evergreen plantations have been planted, thus removing large areas of habitat for black bears.  Conservation efforts in Japan are critically important; if bears can coexist with such high densities of human populations, there may be hope for the rest of Asia.

Picture courtesy of Harriet Corbett, Rox Graphics, 866 Rd. 7RP, Powell, WY 82435, 307 645 3202, crowhart@wtp.net